Within the field of (metal) interconnect fabrication in integrated circuits, transition metal layers, such as layers comprising manganese, are very interesting as barrier layers. US20110163062 A1 for example describes the use of manganese, chromium, vanadium or cobalt layers for preventing copper diffusion out of the wires. The significance of these transition metal layers is mainly owed to them being very conformal layers, which are self-forming and which can be scaled down to sub-2 nm thickness.
These transition metal films may be either in the form of the metallic transition metal or in the form of a transition metal compound. On silicon oxide, the mechanism of manganese barrier formation involves the formation of manganese silicate. On a low-k material however, this is much more difficult, due to a reduced number of available oxygen sites, and only happens upon annealing above 200° C. Furthermore, if the low-k material is porous, manganese easily diffuses into the pores. Apart from diffusion into the low-k material, the manganese also readily diffuses into the copper; resulting in an increased copper resistivity and a loss of barrier properties.